This invention relates to optoelectric devices using compound semiconductors.
Also the conventional compound semiconductor devices are usually formed on(100) crystal substrates, and the threshold current density for lasing is lowered when a quantum well laser is made on a (111) plane according to a recent report [IEEE 45th Annual Device Research Conference, paper VB-1 (1987)].
The present inventors found that the band gap of Ga.sub.0.5 In.sub.0.5 P serving as an active layer of AlGaInP lasers was grown on a (100) plane, where 1.849 eV was obtained, whereas 1.914 eV was obtained when grown on a (111) plane, and thus the lasing wavelength of semiconductor laser could be made by at least 20 nm shorter (M. Kondow et al., 35th Meeting of Japan Applied Society, Abstract 29p-ZE-S, Mar. 29, 1988, JSAP Catalog Number: AP881105-02).
Then it was reported that when a semiconductor laser using AlGaInP crystal was formed on a (100) plane to utilize the aforementioned property, a lasing wavelength of 670-680 nm was obtained, whereas a shorter lasing wavelength, i.e. 649 nm, was obtained when formed on a (111) B plane (M. Ikeda Electron. Lett., 1988, 24, pp 1094-1095).
In a (111) B wafer used in the aforementioned report, {110} planes, i.e. cleaving planes intersect on the (111) B plane at 60.degree. or 120.degree.. That is, when the wafer is to be made into chips by cleaving, it is cleaved into a triangular or rhombic shape. It is inconvenient in handling, if chips of uniform shape are not obtained. If the chips have sharp edges at the corners, such sharp edges are liable to break. Thus, the workability and yield are not good, and thus the productivity is low.
When AlGaInP is doped with zinc to make a p-type crystal, a higher hole concentration than 5.times.10.sup.17 cm.sup.-3 cannot be obtained with a (100) substrate crystal, and further addition of the dopant deteriorates the crystallinity to the contrary. Thus, the hole concentration is not high enough to obtain high-performance, optoelectronic devices. That is, unless a high hole concentration as high as 1.times.10.sup.18 cm.sup.-3 is obtained, an electric resistance remains high and the characteristics and reliability of the devices will be unsatisfactory owing to the heat release.